When Uproar is initially used (i.e. when the user is not already making an uproar), any sleeping Pokémon on the field are woken up (even if they have the Ability Soundproof or are not adjacent to the user). This is now the only time Uproar wakes up Pokémon that are already asleep.

Does uproar do more damage to sleeping Pokémon?

Effect. Uproar deals damage for 2-5 turns. During this time, the user cannot use another move. Uproar will negate any attempts to inflict sleep while its effect applies, and will wake up any sleeping Pokémon on the field when it starts.

Is uproar a good move?

7 Awful: (Uproar, Wood Hammer, Endeavor, Boomburst)

Besides that, a lot of its natural moves aren't anywhere near as effective. Endeavor is extremely hard to make work effectively, Boomburst's damage is based on Rillaboom's terrible Special Attack stat, and Uproar is rarely useful anywhere.